The invention relates to manufacturing annular fiber preforms, in particular porous preforms for constituting the reinforcement of annular parts made of composite material and obtained by densifying preforms with a matrix.
The particular field of application of the invention is making fiber preforms for annular friction parts made of composite material such as clutch disks or brake disks made of thermostructural composite material. Such disks comprise fiber reinforcement, generally made of carbon fibers, densified by a matrix of carbon and/or ceramic.
A method commonly used for making fiber reinforcement for a disk of composite material, in particular for a brake disk of carbon/carbon (C/C) composite material, consists in making an annular preform by stacking plies of two-dimensional fiber fabric.
Suitable two-dimensional fiber fabrics are woven cloth, sheets made up of one-directional fibers, multidirectional sheets made up of a plurality of one-directional sheets superposed in different directions and bonded together, e.g. by needling, layers of felt, or complex fabrics comprising a ply made of a woven cloth or a sheet onto which a layer of felt or of free fibers has been secured, e.g. by needling.
The plies may be superposed flat, while being bonded together by needling, so as to constitute a plate from which annular preforms can be cut out, as described for example in U.S. Pat. Nos. 4,790,052 and 5,792,715. That method is in commonplace and satisfactory use for making preforms for C/C composite material brake disks, but it leads to a large amount of scrap when cutting out the preforms.
Another known method, described in document EP 0 424 988 consists in cutting out annular sectors from two-dimensional plies and in forming an annular preform by superposing and needling rings built up by juxtaposing the sectors. That method serves to reduce the amount of scrap material, but it does not completely eliminate it, and the preforms are more difficult to make.
In order to avoid any scrap material, proposals have been made to produce annular fiber preforms by winding deformed braids or helical cloth so as to form turns that are superposed flat, which turns are bonded together by needling. Reference can be made to U.S. Pat. Nos. 5,662,855 and 6,009,605. Those methods require the use of very particular fiber fabrics—deformable braids or helical woven cloth—that are expensive to make.